Electric resistance unit.



H. W. DENHARD.

. ELECTRIC RES ISTANCE UNIT.

APPLICATION FILED OCT. 31.1911.

1 ,1--1=3,576.v Patented June 15, 1915.1

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TiIdANGISCO, GALIFORNIA, ASSIGNOR TO THE CUTLER- UQ, OF lltXLWJhUKIEE,WISCONSIN, A CORPORATION OF WI$GON$IIL\T.

ELEG' EFRIC EESlEiTANOE UNIT.

teasers.

I It hasaineng its ohgects to proved resistance unit a A further objectoi? my invention is to providelanimproved electric resistance unit of;high heating;- capacity especially adapted provide an irnto nee in'electric heating devices which Z be constructeddna,very compact term,the h at lining evenly distributed to the object to hsheated j (E ther:objects and advantages oi? my improved construction will hereinafterappear. In the:accompanyingdrawings l have, for'parposes ofillustration, shown one form iwniea my invention may assume in practice.

inst-invention, however, is not limited to ithiaform; h-nt' may assumeother forms.

' rhi'gurel shows a top pian view of a unit withithe deter protecting.sheet: removed;

Zshowsatopplan view of thehase member for the unit; Fig". 8 shows a sectional view se a unit in position an iron; Fig. lshowsa plan view of asection of slotted resistance material; 5 shows a perspective view oftheend of the resistance material after it has been folded as shown inglfig. l; T 1

'ln'these drawingsl have for per-poses oi": illiistration shown one formwhich my in- Bimhtioninay assume when applied to a heat element for usein an electric iron. his therein illustrated, tin-insulating hase fl ispreferably co ered with a resistance inaterial :2, which may be formed;in one piece wound lengthwise around said basein such aman ner that aplurality of layersoi "resistance material are provided on each surfaceof the hose the layers oiirroeista-nee material on oneside oi the baselying: op-

posits and in parallel planee-tothose on. the

other side ot'th-e hase, ihe iasnlating hase 1 may he-dorrsedofanysnitabie insulating material .iininrpra- Speeifieation of LettersPatent.

; Patented June 15, 1915.

' Appiication filed flotobcr 31, 1911. Serial No. 657,804.

ferred form I use mica as this insulating material. The resistancematerial 2 may assume variousforms. In. a preferred form, however, Iemploy slotted resistance ribbon. This resistance ribbon is wound uponthe base latter, the manner. of tape, passed up one side of the base anddown the other side in a parallel plane, and substantially opposite thefirst strip until the entire surface of the base is covered as shown inFig. 1. In the construction herein illustrated, the base 1, ismade insuch a shape that it will conform to the opening in the interior of anelectric iron. In order that the resistance material may be suitablywound upon the same and that the strips may be suitably spaced, apart,the base is provided with a plurality of steps 3' in its sides which areeach adapted to receive a strip of theresistance material 2. In orderthat the strips of resistance material may be spaced apart from each;other, suitable projections 4; are preferably provided'in the corners ofthe steps 3 and a projection 5 is provided at the top of the base. In apreferred form, in order to space the strips at the back of the unit, aplurality of spaced projections 6 is provided across the back of thebase as shown in Fig. 2.

In a preferred form, the resistance ma terial is made up from a singlestrip of slotted. resistance ribbon of the type shown in .Fig. 4, andthe end-connections for the same are made by hendingradjacentconvolutionsof this strip in'the manner shown in Fig, 5. When it isdesired to form a unit of the shape shown'in Fig. 1, the halves 7. and 8of a convolution of the slotted resistance ribbon are bent along a linewhich oonsti-' totes a continuation of the slot 9 until these halves 7and8 are substantially parallel to eachother. The part 7 is then bentbachward at right angles ornpward as shown 1n 4 along a longitudinallyextending line 10 and is then again bent along a second longitudinallyextending line 11'. It is thusv seen that, as shown in Fig. n, the twosections of the resistance material may be arranged in parallel planesand connected by a cohnecting strip of unslotted resistance materialwhich constitutes the part '7 shown in Fig. 4, By hendingthe resistancematerial in this improvedmonner, I am able to form a unit'in-which thestrips may be brought on the different sides of the base in. no

provide the desired connections.

parallel rows by using a single strip of slotted resistance ribbon. Noadditional cutting of the resistance material is re quirod and it may bereadily shaped so as to lhus it is seen that the section 7 forms aconnecting strip which may be folded over one of the projections .6 onthe base and that the several strips are effectually spaced by theseprojections. By this improved manner of making up the unit, I am ableto'provide a continuously wound unit in which the strips may be verycompactly arranged so that the heating effect is evenly distributed overthe surface of the object to be heated and in which there is little orno space be tween the strips of resistance material be yond thatnecessary to properly insulate the same from each other.

After the strip of resistance material has been wound or looped upon thebase 1, it is preferably placed between sheets of insulation 12'and 13of a slightly larger size than the base 1 so the unit may he effectuallyinsulated from the interior of the iron. These insulating sheets arepreferably, as in the usual construction, compressed upon the resistancematerial by means of suitable bolts 12, which pass down through the unitand serve to compress the same between the body portion 15 of the ironand the heat retaining or ballast plate 16. In order that the resistanceunit maybe efiectually insulated from these bolts, the perforations 17in the sheets 12 and 13 through which the bolts are passed arepreferably made slightly smaller than the perforations in the base 1. Ifde sired, I may pass these bolts through one or more of the strips ofresistance (material, punching out a portion of the same as shown inFig. 1, and leaving a portion of the strip unslotted adjacent thepunched out portion as shown in that figure.

In order that there may be no short circuiting due to an accidentalcontact at the connection points around the projections 6,

I may if desired clip the corners of the re sistance material as shownat 18 in Fig. 1. Further, in order to provide suitable terminalconnections for the unit, I preferably slightly extend the ends of theresistance material as at 19 and leave these portions nnslotted. Inorder that no short circuiting may occur at these ends, I preferably cutaway a V-shaped portion 20 as shown in Fig. 1. It is of course evidentthat the terminals 19 may be connected in any suitable manner to theline. If desired, for instance, suitable terminal connections or plugsmay be riveted or otherwise secured in perforations 21 in the ends-ofthe same.

By my improved construction I have provided an electric resistance unitin which the resistance material covers substantially the entiresurfaceofthe base and in which the resistance material. may be woundupon both sides of said base, the strips on each side being so closelylocated with respect to each other as to form a practically continuoussheet of resistance, material. By my improved construction, while thesestrips of resistance material are very compactly arranged, they are, atthe same time, afi'ectually insulated from each other and are heldsecurely in position by the base, so that there is no danger ofshort-circuiting. 'By my improved construction I am able to use acontinuous strip of resistance material of the fiat slotted ribbon typeand amthus able to obtain an increased heating effect and, at the sametime, provide a unit which is exceptionally thin, so that it occupiesbut little space and the heat may be transmitted directly to thesurfaceto be heated. 'Further, when the unit is assembled, the parts ofthe same are securely held in position so that the unit is well adaptedtowithstand long use in service. construction I have provided anefficient unit which may be manufactured at small expense.

Further, by my improved one specific form which my invention may assumein practice, I do not wish to be limited to this form, which is shownfor purposes of illustration, but Wish rather to include within thescope ofthis application, all. those forms of my invention fallingwithin its spirit.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A resistance unit comprising a base and a continuous uniform strip ofslotted resistance ribbon formed into a. series of parallel convolutionseach extending completely around a portion of said base and each havingits sections on opposite sides of said base in the same vertical plane.V

2. A resistance unit comprising a base and a continuous uniform strip ofslotted resistance ribbon formed into a series of parallel convolutionseach extending completely around a portion of said base and each havingits sections on opposite sides of said base in the same vertical plane,said base having portions for maintaining adja-' of slotted resistanceribbonwo'und on said n 4'. In anelectric resistance unit, a stepped ofsaid base lie directly opposite the turns on the opposite side and in aparallel plane. 5. In an electric resistance unit, a stepped base,strips of slotted ribbon resistance material positioned on said stepsand insulated from each other, and means connecting the ends of saidstrips for permitting the strips on one side of said base to occupypositions directly opposite the strips on the other side. I r Y 6. Anelectric-resistance unit having an insulating base,acontinuous uniformstrip base with its turns spaced apart, the convolutions of the ribbonformed by the slots being so bent at the end of each turn of the ribbonthat the turns may be connected together by a convolution of the ribbonWith the sides of each turn opposite and parallel to each other. e

7. An electric resistance unit having an insulating base, a continuousuniform strip of slotted resistance ribbon wound on said base with itsturns spaced apart, said rib'- bon being bent back on itself at the endof each turn and folded over laterally whereby one of the convolutionsformed -by the slots is bent back on itself, said convolution beingreversely bent back on itself at its other end whereby the turns areconnected together by said convolution so that they may be wound on thebase with the sides of each turn directly opposite and parallel to eachother.

In witness whereof, I have hereunto subscribed my name in the presenceof two witnesses. I

1 HARRY DENHARD.

Witnesses:

W. L. RooKwELL, GEO. B. Jonas.

